While I was typing the last entry I wondered if there were any websites devoted to old PC technology. My sense of nostalgia overwhelmed me when I visited Old-Computers.com. In particular this article on the IBM PC AT brought it all back. I remember using one of these in school when I was younger. It had the 286 processor (which really kicked ass in its day) an outlandish 1Mb of RAM and 16-bit expansion slots, of course. This had a type 2 mobo with 4 standardised 256k slots instead of 128.. Those were the days.. when computers were dumb, real men used DOS, we played footie in the park, jumpers for goalpsots…
Apparently the 128 k slots were a bit weirder than they seemed initially.
The first AT used 128 k chips, which appeared to be two 64k chips stacked. It used two DMA chips, which tended to fail in tandem. It also used a second IRQ controller. If the AT had more than 640 k of RAM, the CMOS would only allocate the first 512 as Convential, the rest as Extended.
Only 17 hard drive type were supported in the CMOS, causing no end of headaches when Seagate realsed their 40 meg half height. The 1.2 meg floppy drive could read and write 360’s, but if you formatted one, it couldn’t be read by a regular double density drive.